The present invention generally relates to thermal management in electronic devices.
The performance of electronic circuits and their semiconductor devices (xe2x80x9cchipsxe2x80x9d) is limited by temperature. Semiconductor device performance. degrades when the internal temperature reaches or exceeds a particular limit. For example, in silicon integrated circuit devices, for each ten degree centigrade rise in junction temperature, the operating lifetime of the semiconductor device is decreased by a factor of at least two. Demands by OEMs for smaller package sizes and increased device densities has resulted in higher power densities, with the concomitant need for efficient heat dissipation becoming extremely important.
This industry need is compounded, in next generation, highly integrated semiconductor devices by the occurrence of xe2x80x9chot spotsxe2x80x9d, i.e., localized areas on the chip having relatively high thermal energy generation. These hot spots arise at locations on the chip where significant electrical activity occurs, e.g., processor, I/O control circuits, etc. The manner of cooling these devices has depended upon many parameters, including the space available for the cooling process, the temperatures to be encountered, the location(s) of hot spots, and the ability to distribute or xe2x80x9cspreadxe2x80x9d the thermal energy over sufficient surface area to provide for efficient heat transfer. In the past, simply passing a fluid over the device or, over a finned heat sink that is attached to the device, was sufficient to maintain the semiconductor at safe operating temperatures. Different cooling fluids have been used, depending upon the application and the density of the electronic devices in a given circuit. Boiling liquids are often used, such as fluorinated hydrocarbon refrigerants, which are delivered to the semiconductor device in liquid form, and are then boiled to remove heat. These systems often have the highest heat removal rate for a limited area, but require a considerable amount of power to operate, i.e. to be pumped to and from the heat transfer site.
It is also well known in the art to employ micro-pump driven heat exchangers to cool semiconductor devices and packages. For example, U.S. Pat. No. 5,336,062, issued to Richter, discloses a micro miniaturized pump consisting of two superposed, interconnected pump bodies of semiconductor material, which each include electrically conductive regions insulated from one another. This micro miniaturized pump includes a thin, flexible diaphragm having at least one integrated check valve, which has an inlet aperture and a cover plate over it. This pump is adapted for circulatory movement of coolant close to an electronic device. Similar micro miniature pumps are also disclosed in U.S. Pat. Nos. 5,466,932, issued to Young, et al., and 5,529,465, issued to Zengerle, et al.
The Northrop Grummand Corporation owns U.S. Pat. Nos. 5,763,951; 5,801,442; 5,901,037; and 5,998,240, all issued to Hamilton, et al., which disclose various methods of extracting heat from a semiconductor body through the use of micro channels formed in one or more pieces of silicon, and the circulatory movement of a coolant through those micro channels.
U.S. Pat. No. 5,238,056, issued to Scotti, et al., discloses various heat exchange apparatus in which an oscillating flow of primary coolant is used to dissipate an incident heat flux. Here the oscillating flow may be imparted by a reciprocating piston, a double-action twin reciprocating piston, a fluidic oscillator, or a electromagnetic pump.
These and other prior art devices use microstructures positioned close to the surface of a semiconductor device that act as a heat exchanger having coolant circulating through channels to transfer thermal energy away from the semiconductor device and its package, but do not provide an efficient heat spreading mechanism for distributing the thermal energy generated by hot spots on the chip across the package itself. There is a need for a semiconductor packaging structure that efficiently and evenly spreads thermal energy generated by hot spots on a chip across a substantial portion of the package so that the thermal energy may be removed rapidly and effectively from the package.
The present invention is a heat spreader comprising: a plate having a first end and a second end and a plurality of channels therebetween; a reservoir at the first end; and an oscillator for oscillating a fluid between the first and second ends, the oscillator being integrally contained within the plate.